1. Field of the Invention
This invention relates to a light-reflector-type encoding method and the light-reflector-type encoder. More particularly, the invention relates to a method and apparatus for encoding the kinetic variation to be detected of the subject under detection by optical signals, through the motion of a mobile body which moves in response to the motion of said subject, by emitting light from one end of an optical fiber or a bundle of plural optical fibers (which will be hereinafter referred to simply as an optical fiber) on a mobile body which moves in response to the kinetic variation to be detected of the subject under detection, and receiving the light reflected by the mobile body at the same end of said optical fiber.
2. Description of the Related Art
Heretofore, the most generally employed encoder includes a graduated board and electronic parts such as light-emitting and light-receiving elements. This type of encoder has a number of drawbacks. It is easily adversely affected by electric noise, temperature and humidity; it is incapable of precise measurement; requires anti-fire and anti-explosion provisions if it is used in equipments around which use of fire must be avoided; and it is useless for long-distance signal transmission because of the voltage drop or electric distortion.
An optical encoder has been proposed, in which the pulse output is converted to optical signals, in an attempt to eliminate such drawbacks of conventional encoders in which the pulse output is electric signals.
Japanese Official Patent Gazette, Publication No. 52640/82 disclosed an optical encoder comprising a luminous source emitting two-phase rectangular waves having mutually a phase difference of 90.degree. at .omega.-frequency, a code disc with slits to let pass the two types of light beams from said source, the first optical fiber having two front ends to receive a part of the two light beams before they transmit through said slits, a phase board having phase slits which is fixedly disposed paralleling with said code disc and the second optical fiber having two front ends to receive the two light beams transmitted through said phase slits, said two light beams being emitted from said light source against the code disc and received by said front ends of two optical fibers before and after they pass through the code disc and phase board, and the motion of a subject under detection which is connected to said code disc being detected by comparing those quantities of light.
In the optical encoder disclosed in the above noted Publication No. 52640/82, however, optical fibers must be disposed at both front and back of the slitted disc to receive the light beams emitted from the luminous source. This in turn makes it necessary to install near the slitted disc a means for mechanically connecting the slitted disc with the subject under detection, so that the disc can move in relation to the motion of said subject. Installation of such a means causes designing difficulty. Furthermore, because the prior art encoder requires a means for receiving both the emitted light and transmitted light, it can neither be miniaturized nor can perform precise measurement of the subject's motion.
Separately, Laid-Open Patent Publication No. 87,818/81 proposed a light-reflector type encoder which dispensed with the transmitted light or the means to receive that light. However, the encoder disclosed in this publication has other drawbacks. For example, in order to detect the variation in the light-reflectivity to precisely determine the position of the subject under detection with this prior art encoder, a graduated board connected with the subject is used, and a light of the width less than that of the individual graduation is projected and the reflectivity of this light varying with the movement of said graduated board must be detected. Consequently, if the width of graduations is narrowed to improve the precision, the width of the optical fiber for projecting light on the graduations must also be narrowed in response thereto, and also the distance between the end of the optical fiber and the moving graduated board must be precisely controlled to regulate the extremely fine light-emitted area.
As the width of the optical fiber is lessened, however, the transmission of effective quantity of light becomes more difficult, increasing the difficulty in precise positional detection. Again, when the graduation width is drastically narrowed, it becomes difficult or impossible to give identical width, form and reflectivity to all of the great number of graduations on the board, which obviously renders the precise positional detection difficult.